20. November 2003

Bayer and Onyx Announce New Data on Dual Mechanism of Action of BAY 43-9006

Updated Phase II Data Evaluating Novel Signal Transduction Inhibitor in Kidney Cancer Also Released

WEST HAVEN, CT and RICHMOND, CA - Bayer Pharmaceuticals Corporation (NYSE: BAY)
and Onyx Pharmaceuticals, Inc. (Nasdaq: ONXX) announced today new preclinical
data on the proposed anti-tumor activity of the investigational drug BAY
43-9006, indicating that the novel signal transduction inhibitor exhibits a
dual mechanism of action targeting both cell proliferation and angiogenesis
(the formation of new blood vessels to support cancer cell growth). The data
were presented at the American Association for Cancer Research-National Cancer
Institute-European Organization for Research and Treatment of Cancer
(AACR-NCI-EORTC) meeting in Boston, USA.

BAY 43-9006 is the first compound that is known to target both Raf kinase and
VEGFR2 to inhibit two essential mechanisms involved in tumor growth. Raf
kinase is a key enzyme in an important growth signaling pathway associated with
the proliferation of tumor cells. VEGFR2 is a main receptor of the vascular
endothelial growth factor (VEGF), which plays a key role in angiogenesis.

Additionally, updated Phase II clinical data was presented at the meeting,
evaluating BAY 43-9006 as a potential treatment of advanced renal cell
carcinoma (RCC, or kidney cancer).

"BAY 43-9006 exhibits dual activity in important mechanisms that inhibit cancer
progression. These findings suggest that BAY 43-9006 may have a potential role
in the treatment of a range of cancers," said Susan Kelley, M.D., vice
president, Oncology, Bayer Pharmaceuticals Corporation. "Besides kidney cancer,
Bayer and Onyx are also evaluating this novel compound as a treatment for
melanoma, liver, pancreatic and other cancers."

Interim Phase II Study Results
Bayer and Onyx also released an updated data analysis of Phase II clinical
results that were first presented in October 2003. The updated data analysis
included 50 participants with advanced and progressive RCC who were evaluable
after 12 weeks of treatment. Of the evaluable patients, 42 percent (21
patients) had tumor shrinkage of at least 25 percent at the week 12 assessment.
Twenty-six percent (13 patients) had their tumors stabilized within 25 percent
of pretreatment size. Overall, 68 percent (34 patients) of this cohort of study
participants did not demonstrate tumor progression by the 12-week evaluation
point, as assessed by the physicians conducting the clinical trial. The
remaining 32 percent (16 patients) discontinued study treatment either because
of progressive disease or adverse effects. These early data are subject to
confirmation and to a final independent review at the conclusion of the study,
at which time the final results will be released.

The five-center, Phase II randomized discontinuation study incorporates a study
design that consists of two phases: a 12-week induction phase followed by a
randomization phase. During the induction phase, all study participants
received BAY 43-9006 orally at 400mg twice a day, administered as a single

"BAY 43-9006 continues to demonstrate potential as a treatment for patients
with progressive renal cell carcinoma, with a frequency of tumor shrinkage and
disease stabilization rates that remain encouraging as we analyze additional
patient experience from this clinical trial," said Mark J. Ratain, M.D., the
Phase II study's lead investigator and professor of medicine and associate
director for Clinical Sciences, Cancer Research Center, University of Chicago,

All patients with RCC who participated in the trial had progressive disease on
study entry. In the study, the most commonly reported drug-related events
include: mild-to-moderate hand-foot syndrome, rash, diarrhea, and hypertension,
which were shown to be manageable and reversible.

The participants in this study with RCC are part of a larger study population,
which totals 342 participants, with advanced refractory solid tumors of
multiple types, including RCC (73), melanoma (31), colorectal (115) and others
(123) including pancreas, ovarian and breast carcinoma.

Based on the results observed in kidney cancer, Bayer and Onyx have begun an
international, multi-center Phase III trial to further evaluate the safety and
efficacy of BAY 43-9006. More than 800 people with advanced renal cell
carcinoma will participate in the Phase lll study at sites worldwide. The
primary objective of this randomized study is to confirm the early suggestions
of clinical activity of BAY 43-9006 in RCC, using improvement in survival as
the primary endpoint for assessment of clinical benefit. The study also will
assess time-to-tumor progression, overall response rate, quality of life and
the pharmacokinetics of BAY 43-9006.

In other clinical studies, BAY 43-9006 is being evaluated in a Phase II study
in participants who have advanced hepatocellular carcinoma (liver cancer), as
well as in eight ongoing Phase Ib studies where BAY 43-9006 is combined with
standard cytotoxic chemotherapeutic agents. In preliminary findings reported to
date, preliminary anti-cancer activity has been observed across a number of
tumor types.

BAY 43-9006 Mechanism of Action
BAY 43-9006, an investigational novel signal transduction inhibitor, is the
first compound to target both the Raf/MEK/ERK pathway to inhibit tumor cell
proliferation and the VEGFR-2 signaling cascade to inhibit tumor angiogenesis.

The Raf/MEK/ERK signalling pathway is an important mediator of responses to
growth factors. Activation of growth factor receptors leads to subsequent
activation of the MAP kinase pathway downstream of Raf kinase, leading to cell
proliferation. Inhibition of the MAP kinase pathway through inhibition of Raf
kinase most likely results in anti-proliferative effects with slowing or
inhibition of tumor cell proliferation.

In endothelial cells, BAY 43-9006 exerts an anti-proliferative effect by
blocking the VEGFR-2 pathway at two levels: upstream by inhibiting the VEGFR-2
receptor and downstream at the level of Raf kinase. It is believed that these
activities lead to anti-angiogenesis activity.

"With its dual mechanism of action, BAY 43-9006 may provide an important new
approach for treating kidney cancer, a treatment area where there is
significant unmet medical need," said Dr Scott Wilhelm, associate director
Oncology, Bayer Pharmaceuticals Corporation.

About Kidney Cancer
Renal cell carcinoma is the most common form of kidney cancer. Despite advances
in understanding the growth mechanisms of many different tumor types, kidney
cancer is still not fully understood. It is believed that both the Ras
signaling pathway and angiogenesis may play a role in kidney cancer.

Currently, median survival for patients with advanced metastatic kidney cancer
is estimated at eight to 12 months, with five-year survival of less than 10
percent.1,2 Approximately 190,000 people worldwide are diagnosed with kidney
cancer each year, and over 91,000 die from the disease annually.3

The primary therapy for localized kidney cancer is surgery.4 Advanced kidney
cancer is generally resistant to chemotherapy treatment, with reported response
rates (50 percent shrinkage) of less than 10 percent.2,5 Immune modulators,
such as interferon-alpha and interleukin-2 (IL-2), are currently used as
systemic treatment for some patients with advanced disease, but response rates
remain low, at about 15 percent. Occasionally, a few patients undergoing
systemic therapy do experience long-lasting remission.6,7,8,9 However, the
toxicity of high-dose IL-2, the only treatment approved for the treatment of
advanced kidney cancer, limits its use.10,11

About Bayer and Onyx Co-development Collaboration
BAY 43-9006 is being co-developed by Bayer and Onyx. The co-development
collaboration results in Onyx funding 50 percent of the development and
marketing costs for BAY 43-9006. In return, Onyx has a 50/50 profit share in
the United States, where the companies can co-promote the product. Everywhere
else in the world except Japan, Onyx's share is less than 50 percent, since
Bayer has exclusive marketing rights. In Japan, Bayer will fund product
development, and Onyx will receive a royalty.

About Onyx Pharmaceuticals
Onyx Pharmaceuticals is engaged in the development of novel cancer therapies
that target the molecular basis of cancer. With its partners, the company is
developing small molecule drugs. One of these drugs, BAY 43-9006, is in
co-development with Bayer Pharmaceuticals Corporation. For more information
about Onyx's pipeline and activities, visit the company's website at

About Bayer Pharmaceuticals Corporation
Bayer Pharmaceuticals Corporation is part of the worldwide operations of Bayer
HealthCare, a subgroup of Bayer AG. Bayer HealthCare is one of the world's
leading innovators in the health care and medical products industry.

Bayer HealthCare combines the global activities of the business groups of Bayer
AG in the fields of Biological Products, Consumer Care, Diagnostics, Animal
Health and Pharmaceuticals. More than 34,000 employees support the worldwide
operations of Bayer HealthCare.

Our work at Bayer HealthCare is to discover, manufacture and market innovative
products for the purpose of improving human and animal health worldwide. Our
products enhance well being and quality of life by diagnosing, preventing and
treating disease.


1 Glaspy JA. Therapeutic options in the management of renal cell carcinoma.
Semin Oncol 2002 Jun; 29(3 Suppl 7): pp 41-46

2 Motzer RJ Survival and Prognostic Stratification of 670 patients with
Advanced Renal Cell Carcinoma. Journal of Clinical Oncology, Vol 17, No 8
(August), 1999: pp 2530-2540.

3 WHO (Globocan 2000)

4 National Cancer Institute. Available at
www.meb.uni-bonn.de/cancer.gov/CDR0000062894.html. Assessed October 13,

5 Yagoda A. Chemotherapy for advanced renal-cell carcinoma: 1983-1993. Seminars
in Oncology. 1995: 22 (1): 42-60

6 Krown SE. Interferon treatment of renal cell carcinoma: Current status and
future prospects. Cancer 1987; 59: 647-651

7 Muss HB. The role of biological response modifiers in metastatic renal cell
carcinoma. Seminars in Oncology. 1998; 15 (5, Suppl 5): 30-34

8 Linehan WM. Cancer of the kidney and ureter. In cancer: Principle and
practice of Oncology (DeVita VT, Hellman S, Rosenberg SA, eds).
Lippincott-Raven Publishers. New York 1997

9 Rosenberg SA. A progress report on the treatment of 157 patients with
advanced cancer using lymphokine-activated killer cells and interleukin-2
high-dose or interleukin-2 alone. N Engl J Med. 1987; 316: 889-897

10 Kammula US. Trends in the safety of high dose bolus interleukin-2
administration in patients with metastatic cancer. Cancer, 1998; 83: 797-805.

11 Stadler WM. Low-dose interleukin-2 in the treatment of metastatic renal-cell
carcinoma. Seminars in Oncology. 1995; 22: 67-73.

Forward-looking statements<br/>
This news release contains forward-looking statements based on current
assumptions and forecasts made by Bayer Group management. Various known and
unknown risks, uncertainties and other factors could lead to material
differences between the actual future results, financial situation, development
or performance of the company and the estimates given here. These factors
include those discussed in our public reports filed with the Frankfurt Stock
Exchange and with the U.S. Securities and Exchange Commission (including our
Form 20-F). The company assumes no liability whatsoever to update these
forward-looking statements or to conform them to future events or developments.